Using a New CRISPR Approach to Rescue the Effects of Autism Risk Genes

Dr. George Chen

The Geschwind Lab continues to develop insights into the molecular mechanisms of different genetic forms of autism spectrum disorder (ASD). Previous research in the lab used families with one or more affected children to identify de novo mutations (alterations in genes that newly arise in the child and are not present in either parent’s DNA) that increase ASD risk, which account for approximately 20% of ASD cases. The majority of these mutations are either known to or predicted to lead to the loss of one copy of the gene (of the two normally inherited). This in turn leads to disease through a condition called haploinsufficiency, in which a single copy of a functional gene is not enough to maintain normal function. The Geschwind Lab is now exploring the possibility that the effects of these haploinsufficient mutations on high-risk ASD genes could be ameliorated by activating the non-mutant copy of the gene to restore expression to normal levels. To do so, the lab is employing a recent advance in gene editing technology known as CRISPR-A.

CRISPR gene editing technologies have made the news over the last few years as a precise means of editing the genome. Unlike the traditional CRISPR/Cas9 system, CRISPR-A uses the precise gene targeting capabilities of CRISPR without editing the genome; rather, it directs a cell’s gene activation machinery to a specified gene of interest. To precisely control the level of gene activation, the laboratory has developed gene activation constructs to target regions of DNA known as enhancers that will turn up the expression of high confidence ASD genes. This approach takes advantage of native DNA elements that control gene expression without editing the genome or relying on artificial gene constructs that could overexpress the gene of interest. These gene activation CRISPRs will be tested in stem cell-based 3D human cultures called cortical spheroids (hCS), which have been shown to recapitulate many features of organismal brain development.

The hCS system enables researchers to model brain development in vitro and study how this complex process is altered by specific genetic mutations or neurodevelopmental disorders. Using this system, the lab will determine if gene activation techniques are capable of reversing the effects of mutations to ASD risk genes to restore normal development and function. To accomplish this work, George Chen, the post-doctoral fellow leading this work, and Dr. Geschwind were recently awarded two pilot grants to pursue this work. The first grant, from the UCLA Broad Stem Cell Research Center, will focus on two established haploinsufficient stem cell lines for ASD risk genes CHD8 and SCN2A. The second grant, from the Simons Foundation Autism Research Initiative (SFARI), will enable the lab to pursue additional gene targets for which mutant stem cell lines have yet to be established.

Results from this study will enhance understanding of the effects of haploinsufficiency in ASD risk genes, the mechanisms whereby they impact neuronal development, and provide a proof of principle for the use of gene activation as a therapeutic intervention in patients.